ESR's "The Art of Unix Programming" includes a longish section on the history of Unix. For the rest of the book, he talks about the Unix programming philosophy,

ESR's "The Art of Unix Programming" includes a longish section on the history of Unix. For the rest of the book, he talks about the Unix programming philosophy, including many examples of real-life software. I found this a fascinating book to learn about the mindset behind Unix, also to compare what that mindset was like back in the 70s (and why) and how it is today. Well worth reading!